Flacco, so the numbers say, is a mediocre quarterback. Per Pro Football Reference, Flacco was ranked 14th in yards, 17th in touchdowns, 19th in completion percentage,15th in adjusted net yards per attempt and 22nd in ESPN's total QBR.

Meanwhile, the 49ers defense is a fortress, allowing just 17.1 points per game. The Niners have the second-best scoring defense, third-best yardage defense, ranked fourth in adjusted net yards per attempt allowed and eighth in turnover differential.

But the playoffs have revealed a Joe Flacco who wins games with huge plays in the fourth quarter, and the 49ers defense has allowed 24 points in both of its playoff games. To find out which unit will prevail in Super BowlXLVII, we'll need to look deeper at the players, schemes and matchups.

The Schemes

The Ravens run what might be considered a traditional, pro-style offense. They often feature two- and three-receiver sets and a tight end and/or fullback.

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Before the midseason firing of former offensive coordinator Cam Cameron, they ran more three and four-receiver sets and called passes more often. After Cameron's dismissal and the promotion of Jim Caldwell, the Ravens focused more on their powerful tailback duo.

The 49ers defense is drawn up by Vic Fangio, a disciple of Green Bay Packers defensive coordinator Dom Capers. Fangio uses a “one-gap” 3-4, meaning each member of the front seven is responsible for a single running lane.

This allows the defensive line to be more aggressive and penetrate the offensive line without abandoning their run responsibilities.

When the Ravens Run

The Ravens are going to want to maximize tailbacks Ray Rice and Bernard Pierce. Over three playoff games, they've combined for 91 carries, 416 yards and two touchdowns.

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But if the Ravens run right into the teeth of the 49ers defense, Rice and Pierce will struggle to get anywhere. The 49ers have one of the best run-stopping defensive ends in football, Justin Smith. Behind him, the 49ers boast two first-team All-Pro inside linebackers, Patrick Willis and NaVorro Bowman.

All told, the 49ers had the fourth-toughest run defense in the NFL this year, allowing just 3.7 yards per carry.

The 49ers can be run on, though. The Seattle Seahawks’ Marshawn Lynch gained 214 yards and a touchdown against the 49ers on 45 carries in two games (4.8 yards per carry).

How’d they do it? Even though Smith only played in the first matchup with Seattle, the Seahawks constructed zone-blocked stretch runs away from him. They also designed tosses and sweeps to get Lynch to the second level of the defense.

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Niners nose tackle Isaac Sopoaga and defensive end Ray McDonald aren’t as stout against the run as Smith, and don’t have Smith’s athleticism. The Ravens also use zone blocking up front and have All-Pro left guard Marshal Yanda to lead the way.

Watch for the Ravens to get the 49ers defense running sideways, then have Rice and Pierce cut back upfield for big yardage.

If the 49ers line can maintain their gap responsibility on the move better than they did against the Seahawks, or if they can bring a safety up to help on the back side, they could shut the Ravens' run game down completely.

When the Ravens Pass

Flacco has been winning playoff games with big plays in the second half. That’s been possible because Flaccohasn’t been losing games with big mistakes in the first half.

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Flacco, as the numbers show, has a low completion percentage and a high yards-per-completion average (12.0, tied with Tom Brady for 10th). This means he’s completing fewer passes, but when he connects they’re further downfield.

Flacco struggles in the short passing game due to his accuracy problems. Caldwell minimizes the risk of turnovers by having Flacco throw short and toward the sideline early; if Flacco misses, it tends to sail out of bounds. In fact, Flacco’s interception percentage is a tiny 1.9; he tied Peyton Manning and Nick Foles for the fifth-lowest rate of pass attempts picked.

By playing it conservatively, the Ravens offense has gotten off to slow starts but has also avoided backbreaking turnovers. If Flacco looks sharp early, the Ravens could open up the throttle and attack downfield. If he throws an early interception, the Ravens could be in deep trouble.

The 49ers pass rush will be the biggest wild card in this game.

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The Ravens' pass protection has been poor all season; their pass blocking was graded 19th by Pro Football Focus (subscription required). The 49ers’ featured pass-rusher, Aldon Smith, racked up an amazing 19.5 official sacks but hasn’t registered a single one in the 49ers’ last five games.

Smith accounted for half the 49ers’ 38 regular-season sacks. Without any from him, the 49ers have registered just one sack in each of their two playoff games.

As Football Outsiders broke down, the combination of Aldon Smith and Justin Smith poses huge problems for any team’s left tackle. The Ravens’ Bryant McKinnie will need to play one of the best games of his recent career for Flacco to be able to consistently throw downfield.

Keys to Watch in Super Bowl XLVII

Whether Flacco is accurate on short passes

Whether Rice and Pierce can get to the second level early

Whether the 49ers' Smiths (Justin and Aldon) can beat the Ravens’ protection

Whether Ravens receivers Torrey Smith and Jacoby Jones can get open along the sideline

Who Will Prevail?

There's no question the 49ers were the better team in the regular season. There's no question that if both teams play their best, the 49ers have the advantage.

The Ravens' biggest strengths match up well against the 49ers' few weaknesses, though, and Super Bowls rarely follow the script. The Ravens run game will succeed early, and that should open up the big-play passing game late.